Journal of Virology, April 2001, p. 3719-3730, Vol. 75, No. 8
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.8.3719-3730.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Department of Molecular Genetics and Microbiology, State University of New York at Stony Brook, Stony Brook, New York 11794-5222
Received 12 January 2001/Accepted 22 January 2001
Internal ribosomal entry sites (IRESs) of certain plus-strand RNA
viruses direct cap-independent initiation of protein synthesis both in
vitro and in vivo, as can be shown with artificial dicistronic mRNAs or
with chimeric viral genomes in which IRES elements were exchanged from
one virus to another. Whereas IRESs of picornaviruses can be readily
analyzed in the context of their cognate genome by genetics, the IRES
of hepatitis C virus (HCV), a Hepacivirus belonging to
Flaviviridae, cannot as yet be subjected to such analyses
because of difficulties in propagating HCV in tissue culture or in
experimental animals. This enigma has been overcome by constructing a
poliovirus (PV) whose translation is controled by the HCV IRES. Within
the PV/HCV chimera, the HCV IRES has been subjected to systematic 5'
deletion analyses to yield a virus (P/H710-d40) whose replication
kinetics match that of the parental poliovirus type 1 (Mahoney).
Genetic analyses of the HCV IRES in P/H710-d40 have confirmed that the
5' border maps to domain II, thereby supporting the validity of the
experimental approach applied here. Additional genetic experiments have
provided evidence for a novel structural region within domain II.
Arguments that the phenotypes observed with the mutant chimera relate
solely to impaired genome replication rather than deficiencies in
translation have been dispelled by constructing novel dicistronic
poliovirus replicons with the gene order
[PV]cloverleaf-[HCV]IRES-
core-R-Luc-[PV]IRES-F-Luc-P2,3-3'NTR, which have allowed the measurement of HCV IRES-dependent translation independently from the replication of the replicon RNA.
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